The evolution of cellular communications has resulted in a proliferation of networks of different technologies and corresponding different air interfaces. As a result, during the course of a single communication session, a wireless mobile station may roam among multiple networks, wherein each such network implements a different technology than the other networks of the multiple networks. Among the different network technologies are third generation (3G) technologies, for example, 3GPP (Third Generation Partnership Project) technologies such as UMTS (Universal Mobile Telecommunication System) and its derivatives such as 3GPP LTE (Long Term Evolution), 3GPP2 technologies such as CDMA (Code Division Multiple Access) 2000 1XEVDO (Evolution Data Only) (also referred to as 3GPP2 HRPD (High Rate Packet Data)), and various OFDM (Orthogonal Frequency Division Multiplexing) technologies such as IEEE (Institute of Electrical and Electronics Engineers) 802.xx systems, for example, networks operating pursuant to the 802.11, 802.15, 802.16, or 802.20 standards.
A multi-mode mobile station (MS) supports two or more air interface technologies. As the MS roams among networks supporting different technologies and air interfaces, it may be beneficial to system performance to handoff the MS from one such network to another. If the MS contains a separate, complete implementation of each air interface technology, then handoff can be accomplished without interaction between the base stations of the two technologies. This is because the connection to the new air interface technology can progress independently of the old connection to the old air interface technology. This requires no change to the specification of either technology because the handoff is handled completely by the MS without network involvement.
It is likely that the designer of a multi-mode MS, in an effort to minimize cost, will attempt to share some components among two or more of the air interface technologies. For example, a cellular phone that implements two technologies might be capable of receiving on both simultaneously but is only able to transmit on one at a time due to sharing the same transmit chain. Even if there were two separate transmit chains, it may still be desirable to transmit on only one at a time to minimize radio frequency interference between the two. However, a sharing of transmit or receive chains in an MS can result in a handoff delay as the MS alternates communicating with each of a source network and a target network. For real-time applications such as Voice-over-Internet Protocol (VoIP), it is desirable to minimize the total handoff time to make the user experience as seamless as possible.
Therefore, a need exists for a method and apparatus for an inter-technology handoff that minimizes a total handoff time of an inter-technology handoff of a multi-mode MS.
One of ordinary skill in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.